How to Winterize Your Sprinkler System

Freezing temps can crack backflows, valves, and underground lines in a single night—water expands about 9% when it freezes—leading to leaks, costly repairs, and spring headaches. Winterizing your sprinkler system protects the backflow (and your water supply), prevents split pipes and flooded valve boxes, extends equipment life, and makes spring start-up fast and stress-free. Whether you choose a simple gravity drain or a controlled air blow-out, shutting off the supply, draining lines, and covering the backflow are quick steps that save money and help you stay code- and insurance-friendly all winter.

The good news: with a quick shut-down and either a manual drain or controlled blow-out, you can protect your system in under an hour.

Before You Start

• Pick your method: Manual drain (gravity) or controlled air blow-out.
• Know your backflow: PVB/RP/DC assemblies need to be drained and protected—never push high pressure air through the backflow.
• Controller: Put your timer on “Rain/Standby” or OFF so the system stays shut down after winterizing.
• Safety: Wear eye protection; if you’re unsure about air pressure or gas/power connections to pumps, hire a pro.

Step 1 — Shut Off & Isolate

1. Close the irrigation main shutoff feeding the system (usually near the backflow or inside the house).
2. If you have a backflow/vacuum breaker, turn the two shutoff handles to OFF, then open the test cocks ¼–½ turn to vent.
3. Open at least one zone valve or manual drain to relieve pressure.

Step 2 — Drain Method (No Compressor)

• Open all manual drain valves at low points and end-caps on lateral lines; let them trickle until empty.
• At the backflow, leave test cocks angled downward to finish draining; set both shutoff handles at ~45° so trapped water can expand.
• Cap/close drains once empty; leave the controller OFF.

Step 3 — Controlled Blow-Out Method

1. Attach a blow-out adapter at the manifold or a threaded port downstream of the backflow.
2. Hook up a compressor with a pressure regulator. Start at ~40 PSI; increase slightly if needed.
3. Run one zone at a time from the controller. Let it blow until only a fine mist appears (usually 1–3 minutes per zone). Don’t run solenoids dry for long; cycle through zones.
4. When finished, close the adapter, vent any residual air, and disconnect the compressor.

Step 4 — Protect the Backflow/Vacuum Breaker

• Confirm the backflow body and bonnets are fully drained (use the test cocks).
• Slip on an insulated cover and seal drafts from below. In very cold/windy areas, consider a listed enclosure or heat-tape solution per instructions.

Quick Reference Table

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Spring Start-Up (Save This)

• Close all test cocks/drains; open isolation valves slowly.
• Pressurize one zone at a time; check for leaks at valves and the backflow bonnet/poppet.
• Flush lines briefly with heads removed if you see debris; then reinstall and set your seasonal watering schedule.

Code note: Always follow local plumbing codes and manufacturer instructions. If you’re on a shared/commercial system, a certified backflow tester may be required.